Why is it not recommended to trade hats for weapons or vice versa?

I've often traded a hat for 4-5 weapons, and afterwards people told me I shouldn't do that, and that it isn't recommended. I wasn't given an explanation.

Could anyone shed some light on this? Why isn't it recommended to trade hats for weapons?

Related question: How do I determine what my TF2 items are worth?

Solution 1:

Hats are worth way more than 4-5 weapons.

For example, according to the TF2 Community Items & Hats Pricing Guide, the relatively common Buckaroos Hat is worth 1⅓ refined metal. One refined metal is 18 weapons.

The pricing guide is only a guideline, but you're still way underpricing yourself.

Solution 2:

I can only imagine that the hat takes more than 4-5 weapons to craft. Taking into account you have to smelt 2 class weapons into 1 scrap metal, then 3 scrap to 1 reclaimed, then 3 reclaimed into 1 refined.

http://tf2wiki.net/wiki/crafting#Metal

A hat takes 3 refined metal, so that's way more than 4-5 weapons. Sorry my math is poor, but hopefully you can see that 4-5 weapons will only net you 2 scrap metal.

Thankfully the math has been done for me by Jon!